The present invention relates generally to fluid transfer systems, and more particularly to systems for transferring fluids in a zero gravity environment.
In space (i.e., beyond the earth""s atmosphere), the transfer of fluids, such as propellants and reactants, will be required to replenish space based propulsion and power generation systems. For example, re-supply of fuel to the International Space Station""s (ISS) attitude propulsion system from a space shuttle may be provided. The ISS attitude propulsion system corrects for atmospheric drag and disturbances resulting from shuttle orbiter docking over the life of the space station. In addition to the ISS application, space based fuel storage depots with propellant transfer capability will be required to fuel reusable upper stages, as well as to fuel space based transfer vehicles in support of future human exploration and development of space (HEDS).
Fluid transfer, including for example, propellant and reactant transfer operation, requires reducing the pressure of a receiver tank through gaseous venting in order to achieve a high liquid fill level. Gaseous venting of a tank in a zero gravity space environment is difficult to achieve because the specific location of the liquid and vapor in the tank is typically not known. In order to provide gaseous venting in a zero gravity atmosphere, a separation of the liquid phase (i.e., liquid content) from the non-condensible pressurant gas (i.e., vapor) is required to prevent the loss of liquid propellant or reactant and maximize tank storage levels. In particular, liquid-vapor separation is needed to efficiently transfer and maximize storage of fluids, such as liquid propellants, in space.
Present liquid-vapor separation systems provide for propellant transfer in space using centrifugal force to separate the denser liquid phase from the lighter gas. The centrifugal force causes the liquid to move to the outside of a mechanism creating the force, where it is collected and returned to the tank, leaving the lighter gas in the center of the mechanism. The center gaseous core is subsequently vented outside the tank. These systems provide acceptable operation in low liquid quality applications (e.g., liquid droplets in vapor) wherein the majority of the volumetric flow is made up of gas. However, a centrifugal type system does not operate properly if the fluid comprises primarily a liquid. Further, in a zero gravity environment, problems arise in such systems, including the possibility of liquid phase moving to the vent line inlet, thereby making this type of liquid-vapor separation system ineffective.
Thus, a need exists for a liquid-vapor separation system for use in transferring fluids, and particularly fluids that are primarily liquid (e.g., propellants, reactants and coolants), in a zero gravity environment.
The present invention provides a system and method for separating the liquid and gaseous parts or phases of fluids (e.g., propellants, reactants and coolants), particularly fluids that are primarily liquid, in a zero gravity environment, through the freezing of the liquid phase. Generally, using a freezing process, liquid within a storage container (e.g., a tank) or similar device is caused to migrate to the storage container wall where the liquid is solidified. After the liquid is solidified, which is provided through the removal of heat from the storage container, non-condensible gas (e.g., pressurant gas) remaining in the storage container can be vented outside (i.e., to space) the storage container without loss of the liquid (e.g., frozen propellant, reactant and/or coolant). The present invention also provides for purging non-condensible gases from inside liquid acquisition screens and enables the filling of capillary devices with liquid.
Specifically, a zero gravity liquid-vapor separation system of the present invention is adapted for use in transferring and storing fluids, including for example, propellants that are primarily liquid, in a zero gravity environment. The zero gravity liquid-vapor separation system includes a heat exchanger for lowering the temperature of a container below a freezing point of a fluid (e.g., propellant, reactant and/or coolant) therein and a vent for use in removing non-condensible gas (e.g., pressurant) within the container when the fluid is below its freezing point.
Further, the heat exchanger may include a cooling loop with a radiator for cooling the fluid within the container, or, alternately, may include a plurality of louver type members for providing cooling. A diffuser may be used in combination with the vent for venting the container. A heater may be provided in combination with the container for heating the frozen fluid (e.g., frozen propellant, reactant and/or coolant) to a liquid temperature point after venting the non-condensible gas.
The present invention also provides a method of transferring a fluid (e.g., propellant, reactant and/or coolant) that is primarily or substantially liquid to a container having residual fluid therein in a zero gravity environment. The method includes lowering the temperature of the residual fluid below the freezing point of the residual fluid, venting the container to remove any non-frozen substances (e.g., non-condensible gases) remaining in the container, raising the temperature of the residual fluid to a liquid point of the residual fluid, and filling the container with additional fluid, such as, for example, a propellant.
Thus, the present invention provides a system and method for transferring a fluid (e.g., primarily liquid propellant, reactant and/or coolant) in a zero gravity environment, such that the storage capacity of the receiving container is maximized. Further, venting according to the present invention provides for removing dissolved gas containments from the liquid and results in a gas free liquid prior to filling or refilling the receiving container.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.